The molding of a composite body by using prepreg sheets generally comprises placing the prepreg sheets on a molding die, overlapping a parting film and a breather mat onto the prepreg sheets, covering them with a pressing bagging film, evacuating the pressing bagging film, and heating the prepreg sheets while pressing. The prepreg sheets are closely attached to the molding die by evacuation, so that they are cured in a shape in agreement with the die.
The pressing bagging film used for covering the prepreg sheets is not so extendable that the pressing bagging film should be provided with wrinkles in advance, to conduct the bagging of the prepreg sheets deformed to a shape along the molding die. Without sufficient wrinkles, too much tension may be applied to the pressing bagging film during evacuation, resulting in breakage. Thus, sufficient wrinkles are indispensable. The bagging is usually a manual operation, which is extremely complicated and thus costly. To produce a molded composite body with a complicated three-dimensional shape, the formation of wrinkles particularly takes time and skill. Further, because the bagging film is disposable, each molding costs the bagging film.
JP2001-47507A discloses a silicone rubber sheet used for molding a composite body in an autoclave, which is three-dimensionally shaped along the molded composite body in advance. To mold the composite body, a prepreg placed on a molding surface of a lower die part for producing the composite body is covered with a silicone rubber sheet, the silicone rubber sheet attached to the lower die part is evacuated, and the prepreg is cured by an autoclave method. The use of a silicone rubber sheet molded in advance makes it unnecessary to provide the bagging film with a three-dimensional shape with wrinkles, resulting in decrease in the number of steps. Because the silicone rubber sheet is reusable, this method is inexpensive.
However, the production of the molding silicone rubber sheet generally comprises attaching an uncured silicone rubber sheet to a wood die for exclusively molding the silicone rubber sheet, which is slightly larger than a lower die part for molding the composite body, and curing the uncured silicone rubber sheet. Thus, this method is costly because of needing the wood die. Because the curing of the silicone rubber causes shrinkage of about 2.5%, a composite body-molding die cannot be used to mold the silicone rubber sheet. In addition, much time and skill are needed to attach the uncured silicone rubber in uniform thickness to the wood die, resulting in high production cost. When an uncured silicone rubber is attached to a composite body produced by using a bagging film and cured in an autoclave, etc. as described in JP2001-47507A, the attaching operation of the silicone rubber is still needed despite that an exclusive molding die is not needed, and a composite body should be molded by using a bagging film in advance. In this case, too, many steps are needed, resulting in high cost.